Research activities will be continued on a Xenon fan-beam detector for computerized tomography. This detector provides high-speed data acquisition by accurately measuring each element in a projection simultaneously. For high accuracy and dynamic range, the counting mode will be the subject of further study. Counting rates of 10 to the 6th power to 10 to the 7th power second are required to scan the body in less than 10 seconds. Although Xenon proportional counters have adequate rise time for these count rates, space charge and recombination effects have resulted in saturation problems. A number of new configurations will be studied to eliminate these problems. In addition an integrating mode of operation has been implemented which avoids these problems although it presents some dynamic-range problems. Other areas to be studied are generic to almost all computerized tomography systems. These include the removal of non-linear artifacts caused by spectral shifts and finite beam size. These techniques allow compensating water vessels to be eliminated which cause significant increases of patient radiation. In addition, studies will be performed of optimum reconstructions in the presence of noise. BIBLIOGRAPHIC REFERENCES: "Correction for Spectral Artifacts in X-Ray Computerized Tomography," A. Macovski, R.E. Alvarez, J.L. -H. Chan and J.P. Stonestrom, Proc. of OSA Conf. on Image Processing for 2-D and 3-D Reconstructions from Projections, 1975. "Utilization of Simple Energy Spectrum Measurements in X-Ray Computerized Tomography," R.E. Alvarez and A. Macovski, Proc. of OSA Conf. on Image Processing for 2-D and 3-D Reconstructions from Projections, 1975.